Colloidal particles that make smart polymer composites deform and rotate

All particles experience forces and torques when subjected to electric and/or magnetic fields. Especially strong field-particle interactions characterize colloidal particles showing dielectric- and magnetic properties. In the presence of magnetic- and/or electric field, dielectrophoretic- and magnetophoretic forces and torques acting on particles result in locomotion and structure formation. If the particles are dispersed and stabilized in liquids the rheological behavior of these fluids (electrorheological- and magnetorheological fluids) is strong function of imposed field. If colloidal particles with special electric and magnetic properties are built into flexible polymer matrix, electric-, and magnetic field sensitive polymer gels and elastomers are obtained. The particles couple the shape of the gel (or elastomer) to the external fields. Shape distortion and locomotion occur instantaneously and disappears abruptly when electric- or magnetic field is applied or removed, respectively. This kind of change in the material properties can be applicable to a variety of fields as a new driving mechanism and can be exploited to construct new type of soft actuators sensors, micromachines, biomimetic energy transducing devices, controlled delivery systems as well as micromotors. In this paper a review of most important colloid electric- and magnetic phenomena for uncharged particles are presented. (C) 2011 Elsevier B.V. All rights reserved.